The invention relates to prosthetic devices, and particularly to devices that may be employed to replace damaged corneal tissue.
Corneas are subject to a variety of problems which mandate their surgical replacement. For example, corneas may become scratched or scarred, and are subject to effect by various degenerative diseases. Corneal transplants have become quite common in the United States, particularly with the advent of microsurgery. However, corneal transplantation is sometimes not appropriate for patients with intractable keratopathy, or patients in whom corneal transplants fail in standard graft procedures.
Various devices have been proposed for solving these problems. Such devices, referred to keratoprostheses utilize a central lenticule or optic that can be prepared from polymethylmethacrylate or other physiologically acceptable glass or polymeric material. A device of this type is shown in White, U.S. Pat. No. 4,612,012, issued Sep. 16, 1986, and White, U.S. Pat. No. 5,030,230, issued Jul. 9, 1991.
Another keratoprosthesis having a collar button design is shown in Doane, M. G., Dohlman, C. H. and Bearse, G., Fabrication of a Keratoprostheses, Cornea 1996: 179-184. The latter device is pre-assembled (i.e., before being placed into tissue) and utilizes a mushroom-shaped plastic member having a threaded post, the cap portion of which fits against the front of a patient""s cornea. A second threaded part is threaded onto the post to complete the construction. In use, a small hole is trephined through the center of a patient""s cornea, followed by a limbal incision and a radial connecting slit. The device is slid into place with the rim of corneal tissue captured between the two plates; the cornea is hence fitted around the threaded post between the anterior and posterior plates. The incisions are then sutured shut, but inasmuch as the portion of the incision between the plates cannot readily be sutured shut, it is extremely difficult if not impossible to achieve the liquid-tight junction between the device and the cornea that is essential for success.
In the latter device, the threaded post portion, of course, must be sufficiently long as to extend through the thickness of the patient""s cornea and for a sufficient distance beyond so as to fully receive the internally threaded second member and to avoid cross-threading. The iris of the eye commonly is spaced posteriorly of the posterior surface of the cornea by only a very short distance, e.g., about 1.7 mm, and hence there is a concern that the post may extend too deeply into the eye so that the iris and lens and sometimes parts of the vitreous need to be surgically removed. Moreover, since the parts are simply threaded together, there is always the potential for unthreading of the device and hence loss of the interior portionxe2x80x94the second portionxe2x80x94into the anterior chamber, causing extrusion of the mushroom-shaped portion with consequent severe problems.
It would be desirable to provide a keratoprosthesis that could readily be attached to the corneal rim of a patient""s eye in a water-tight manner, that would avoid immune rejection problems, that would provide a lenticule not subject to extrusion from the patient""s eye, and that would not protrude posteriorly any significant distance into the anterior chamber.
I have found that a transparent, polymeric lenticule having an elongated stem having at one end thereof a dome-shaped extension having an outwardly extending peripheral skirt can be securely fixed within a bore formed in undenatured corneal or other appropriate tissue in a strong and leak-free manner without requiring any radial incision extending into the bore.
In one embodiment, the invention provides a method for installing, in a liquid tight manner within a bore formed in the cornea and having no radial incision intercepting the bore, a transparent, polymeric lenticule having an elongated, smooth (that is, unthreaded) stem bearing at one end thereof a dome-shaped extension having an outwardly extending peripheral skirt. The stem is placed within the bore with the peripheral skirt contacting and overlying the cornea. A ring, preferably of polymeric material, is received coaxially about the end of the stem that protrudes posteriorly from the cornea and is advanced up the stem to firmly capture between it and the skirt the corneal tissue. The ring is attached to the stem, as by use of an adhesive or by solvent or ultrasonic welding or the like, to form a liquid-tight seal between the lenticule and the cornea.
In another embodiment, the invention relates to an implantable lens comprising a transparent, polymeric lenticule having an elongated stem with a generally cylindrical outer surface and a central axis, the stem bearing at one end thereof a dome-shaped extension having a peripheral skirt extending outwardly from the axis beyond the cylindrical surface of the stem. The lens includes an annulus of undenatured tissue, preferably corneal tissue, having a central bore free from intersecting radial incisions and within which the stem is received. The peripheral skirt of the lenticule contacts and overlies a portion of the tissue annulus adjacent the bore, with a portion of the annulus extending outwardly beyond the peripheral skirt for attachment to the rim of a surgically prepared cornea. A ring, preferably of polymeric material, is received coaxially about the second end of the stem and is attached to the stem, as by use of an adhesive or by solvent welding or ultrasonic welding or the like, to capture the tissue annulus between it and the peripheral skirt of the lenticule. The seal thus provided between the lenticule and the tissue annulus is strong and liquid tight.
In a preferred embodiment, a tissue-adherent, biologically acceptable adhesive is disposed between the cylindrical surface of the stem and the bore within which it is received, and forms a strong, liquid-tight seal. The tissue annulus may, if desired, be provided with a series of partial perforations within which the adhesive may flow to provide improved gripping power to the tissue annulus.
In another embodiment, the invention relates to a method for forming an implantable lens prothesis. A transparent polymeric lenticule having an elongated stem with a generally cylindrical outer surface and a central axis is provided, the stem bearing on one end a dome having a peripheral skirt extending outwardly from the axis beyond the cylindrical surface. Implantable tissue (which may be corneal or scleral tissue of the patient, as described further below or which may be from a donor), is provided with a central bore within which the elongated stem is received, the bore being free of intersecting radial incisions. A ring, preferably of polymeric material, is placed coaxially about the second end of the lenticule stem to firmly capture the tissue between the ring and the peripheral skirt, and the ring is adhered to the stem, as by use of solvent, thermal or ultrasonic welding and/or through use of an adhesive. Preferably, a suitable adhesive is disposed between the cylindrical surface of the stem and the bore of the tissue annulus to form a strong, liquid tight seal between the stem and annulus. It is of course desirable, to further avoid rejection problems, to employ an annulus of corneal tissue harvested from the patient himself or herself, and in yet another preferred embodiment of the method, the implantable lens is assembled upon a flap of cornea of the patient that has not been severed completely from the remainder of the cornea.
In the above-described embodiments, removal of the epithelium and preferably also the endothelium and Descemet""s Membrane, from a corneal tissue annulus in those areas that are to be adhered to the lenticule and polymeric ring enable the adhesive to contact the corneal stroma only.